520 STM with video problem

[Charlie_]

I have a US 520STM that has some sort of video problem. When I use RF there is a bar across the screen that slowly scrolls up. The same bar when using RGB scart is like the screen is bent or warped in the bar area. This bar scrolls off the screen at top and after a while reappears at the bottom to start its climb again. When the computer is cold the bar is very big and gets smaller as the machine is used. Also when cold and a game switched to 50hz the screen gets distorted in 4 wide bars across the screen and the monitor drops the picture now and again. When the computer warms up 50hz plays fine but those 4 areas kinda flash gently like the scrolling bar in 60hz.

 

Pictures are better than words so here is a photo album of the problem, RF, RGB, pictures of the board where I see wires were soldered.

This computer had a 1 meg simms upgrade. I removed it but it didnt seem to effect the video problem at all.

I posted all this over at atari-forum but wanted to also put it here.

Any ideas to fix this?

 

http://imageshack.us/g/232/my520stm3.jpg/

[Charlie_]

Problem turned out to be the power supply. I wired it to an old XT power supply and the problem went away.

Here it is being tested, RF in the workshop and RGB and Composite at the desk.